Apparatus and method for graphical to digital conversion



Aug. 1, 1961 F.M.1RAPNE|.L, JR Y ""29948'63f1.

APPARATUS AND urn-son ron 'GRAPHICAL 'ro DIGITAL CONVERSION famosa. :9,1m s I s, u@

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F. M. TRAPNELL, JR

Y APPARATUS ma man PoR man. 'roprcrm convsnsrcu Y med uw. ze. 19:58- 4 sums-suit: I

Aug. l, 1961 Pom s LorTEn scnesn 1,1961 a F. M `|'RA\'r-|l-:l-.ILA.. 2,994,863 APPARATUS AND ETHOD FUR GRAPHICAL TO DIGITAL 0mm l l 1 l #La l 1 l l .J 1 .m l P A 3.9L m SQ...

Gansta-Sunil sind nge. 29, 195e A am..

Aug. l, 1961. I F. M. TRAPNELL, .IR I APPARATUS AND KETHOD FOR GRAPHICAL T0 DIGITAL ma nw; 2s, :ses

MODIFIED BINARY CODED MASK moet 2eme:

Patented au. -1 nel to International Business Machines Co York, NX., n eorporation of New York Filed Dec. 29, 1958, Ser. No. 783,221

9 Chinn. (Cl. 340-347) This invention relates to apparatus and a method for deriving discrete numerical values from a representation of a quantity that varies in a substantially continuous manner over a range of values, and for storing sets of auch values.

More particularly, the invention in some vofits em bodiments relates to means and a method for determining digital values representative of the coordinates of points on a curve, graph or contour, or image thereoffor example, an oscillogram displayed upon the screen of a cathode my oscilloscope.

Generally speaking, the invention employs a combination of mechanical and optical means to select one coordinate, such as the abscissa, of a given point upon the curve and to project a linearly extended image of the point upon an electrooptical system for trarnlating the geometric position of the image into a specific electric response in the electro-optical system, the response rep resentng digitally the other coordinate, in this case the ordinate,`of the given point on the curve. The digitforming system in this case is a converter from light energy to electrical energy.

In an illustrative embodiment shown herein the ap' United Patent "Oedce' v,fz l paredtosomeltandardeetofvaluea,cr

. The apparatus of the invention, from one point of View, may be characterized as a multiple target reading digital camera or general purpose digital camera. As audi, device is generally useful for converting from visual of continuous nature into digital data, or from an analog type of representation to a digital type of replesentation. The term multiple target refers to fact A that one image is formed to represent one coordinate,

paratus of the invention may be regarded as comprising a combination of a camera with special optical properties, a rotatable mirror, a shield member containing a slit, and a collection of photocells behind a coded mask. These elements may also be supplemented by a rotatable storage device in fixed angular relation to the rotatable mirror for storing digital information received from the i photocells.

An astigmatic lens system is employed to produce images of points on a curve that is being exhibited u upon the face of a cathode ray tube. Due to the astigmatic property of the lens system, images of a given luminous point of the curve take the form of a pair of mutually perpendicular lines separated in space. The rays of light emerging from the lens system are thrown upon a rotatable plane mirror, the beam from the minor being directed upon a vertical slit located at the position of the first line image, which image is vertical in the illustrative embodiment. Consequently, the primary focal image of some particular vertical line on the face of the cathode ray tube falls on the vertical slit. Aa the mirror rotates, successive vertical lines of the object fall upon the slit. In terms of the abscissae and ordinates of the curve to be analyzed, the abscissa is selected by the mirror-slit combination. l'he second line image is made to fall uponacodedmask. Thislineimagcilhorimntal and its vertical position on the mask determines which digital value is tobesssignedtotbeordinate of the- The informationstored may then be analyzed or com.

c g., the abscissa, and another image is formed to represent another coordinate eg., the ordinate.

More particularly the device of the invention may he characterized according to the specilic use to which it i put, for example, the embodiment illustrated hem'n it a digitizing read-out device for an oscilloscope or oscillosmph.

The system disclosed has among its advantages the fact that it is capable of permanently recording, aa on a magnetic drum, signals occupying such a wide frequency band, say 300 to 400 megacycles per second, that with presently known techniques such signals can only he eahibited initially by a high speed device such as a cathode ray osc pe.

. Another advantage of the device of the invention i the' use of; a lsingle optical system (lenssplit combination) to generate both the horizontal and vertical A further advantage is tbe direct mechanical emmen-- tion of the rotatable mirror and the magnetic Storage drum. A series of clock pulsas may he recorded on the drum corresponding to angular positionsof the mirra'. Thus each clock pulse marks a unique horizontal inclement of position and controls the lotion of the corre-4 sponding vertical line image upon the slit 3l withoutO resort to any special synchronizing a'rcuits.

A still further advantage is that the photocell iufm tion, which is sampled in accordance with the clock pulses, can be written into a known memory location on, Vthe drum without the need for any memory addressing FIG. 3 is a diagrammatic showing ofla plan View an optical system similar to that employed in the dnbodimentof FIG. l;

PIG. 3A aan elevational fmnrvisw of c coded partly brokenfaway'to show photocells behind the mask;

FIG. 3B is an elevational view of a slottedmfask with a vertical line image indicated schematically in the slotl 'L' F1o. .4 is a detailed nonteievnionn view f a mask suitable for use in aceordane with the The coded mask may have, at'eachverticalui. 4plurality of opaque and transparent portions inval-iol combinations differing from level to level and foaming' :Q Macode,e.g.,abinarycode,torepresentordinatevalnd. r.

'.asdepictingafunction producingfromapointsourcefirstandsecondlineimages spaced apart and angul'arly disposedonetothe other,

dril lenses 23, 2S, of which lens 23 is disposedwith axis vertical and is of greater curvature than lens 25, the latter lens being disposed with axis horizontal. The` lenses 23, 25, are preferably double convex lenses formed with two parabolic cylindrical surfaces arranged back to back.

An opaque mask 28 having a vertical linear slit 30is mounted in the path of the reflected beam from the rotatable mirror at an optical distance from the lens system 22 equal to the primary focal distance f1 of tht` lens system, that is, at the location of the rst line image. In

system 22 positioned to receive light the cathodera'y tube and to direct a, rcsultautlight beam upon n rotatable plane mirror 24 V y on a shaft 26. The lens system 22 is capable of y 3 :,ssesea Piashnremsomvrwefuummnrm dacodedmask; l

nasamspsrusemuednmormmina f.' .fspointetntrcesuchaspointareiormedbythenc-g V and may, for example, comprise a pair of crossed cylin mask 32. As will be explained more fully in conjunction ofthemask28. Thespotiattheintcneetionoftho -cirrveuandthelineisapoimofthecurvetheordinate of whichistobevtnnslated into digital formatthe instantwhcnthelinefallsupontheslitl. i G.3showsinplan'viewthemannerinwhichimages focus location of the coded mask. At positions in the other than the focal positions the image form blurred and roughly rectangular ormoreorlcls shape. ltwillbeseenthattheverticalimagenploiccts;

, lightonthroughtheverticalslltwandthatthehorizontal1f.

image 94 extends horizontally across the face of the coded .Q

with FIGS. 6-8, it is a property of the astigmatic lens system that thecentral ray96fromthesource88pames through both images 92, 94 with the result that if sourceV 88 moves downward, horiiontal image 94 moves correspondingly upward, or vice versa, the ray 96 pivoting about the center point 98 of the lens system. Motion of the vertical image 9,2 takes place within tbe slit 30 during any vertical motion'of the source $8.

the path of the beam beyond the slit 30 is positioned a c oded mask 32 at an optil distance from the lens system 22 equal to the secondary focal distance f, of the lens system, that is, at the location of the second line image. Beyond the coded mask are mounted a plurality of photo'- cells 34, 36, 38, 40, 42, 44 and 46 (FIG. 3B). Each of these photocells is contained in a box of light-proof material indicated at 48, S0, 52, 54, S6, 58 and 60, respectively, the iront of each box being formed by a portion of the mask 32. 1 4

Frxedly mounted upon the shaft 26 is a recorder comprising a magnetic drum type of storage device 62, providing space upon its cylindrical surface for a plurality of recording tracks, including a home pulse track 64, a

clock track 66 and data tracks 68, 70, 72, 74, 76, 78 and $0. Transducing heads, adapted for both reading and writing are contained in a head assembly 82, which may include individual transducing heads for use with the home pulse track, the clock track, and the various data tracks.

The photocells 34, 36, 58, 40, 42, 44, 46 have their outputs connected respectively to a plurality of and circuits 13d, 132, 134, 136, 138, 140, 142. The head tls-- sembly 82 comprises head 150 for use with the home pulse 50 track 64, head 152 for use with clock track 66, and heads 154, 156, 158, 160, 162, 164, 166 for use respectively with.

data tracks 68, 70, 72, 74, 76, 78, 80. A second input connection to each of the and circuits comes from the clock track head 152 via a lead 160. The respective outputs of the and circuits are connected to the data heads 154, 156, 158, 160, 162, 164, 166. The and cir'uu'ts are of any known type, the function of an and circuit being the usual one of producing an output current or potential if and only if a suitable current or potential is present on all of its input circuits. For example, if A and B are suitable inputs respectively for the two input circuits of a given and circuit, then both A and B must be present in onder that there shall be an output produced V-hry the and circuit.

FIG. 2sho`ws theuseful portion ofthefa'ceZ ofthe cathode ray tube 20 displaying a luminous curve 84 representing data which it is desired to reduce to digital form.- Mor'e particularly, the'curve 84 may be regarded 'it-rm where x may be the abscissa and y the corresponding ordinate of any point on the curve and it is desired to obtain in digital form values of v corresponding to values ci z.

- the rotational position of the mirror determining which FIGS. 3A, 4 and 5 show alternative forms of the coded. mask 32 in front view. The face of the mask is divided into horizontal portions which determine for each photocell whether or notlight will be admitted to the cell when the horizontal image line 94 falls upon that particular t horizontal portion of the mask. Any suitable binary code may be used, comprising combinations of opaque and transparent areas in known maner. Using seven photo cells, as illuminated inFIGS. l and 3A, 128 different values of ordinate or y-values may be distinguished. Either more or less than seven photocells may be used according to the degree of resolution desired. 'For'. the sake of clarity in the drawing, FIGS. 4 and 5 showforms which the mask 32 may take when only four photocells are employed, giving a total of sixteen distinguishf able y-values in the case of each of the two figures.

The coded mask 32 in the embodiment illustrated in- FIGS. l' and 3A is.` assumed to consist of 128 distinct horizontal strips varying in vertical position to cover the range of y-values which the curve may exhibit. 'Ik y-value of each vertical position is by a, combination of transparent and opaque portiom which may, for example, represent in binary form integers( from 0 to 127, inclusive. A straight binary code may be i Usedorsomevariationofthestraightbinarycodemay be substituted as desired. In a preferred form, the so. lled Gray binary code is used as illustrated in 1716.5. In this code, adjacent combinations dicr in respect to one digit'only. A's a result, as the horizontal line image moves over the face of the coded mask, only one photocell at a time is aected, the'cell changing either from s conducting to s nonconducting condition or'vice versa. Inter-:nsofeorrespondencesormappings,itwillbe notedthatverticallinesonthefsceofthecathodeny tube map through the rotatable mirror in one to one fashion onto vertical lines on the slotted opaque mask 28 vertical strip will map into the slit 30 at any given instant. t These vertical strips represent small increments Ax, of t potticnalongthehorizontallxisofthefaceofthe.

permitted to pass through the slit. Verticalpositons, or ruines, on the cathode ray tubemap onto unique veri tical positions of the projected horizontal line of'ligbt on the coded mask 32. Ihus the output of the photocells corresponds te the une of yo) selected through the slit 4Silbytlremirrorzll.Y Inthiswaythereareobtained digitized values of y as a function of x, presentedin binary form air-voltage or current states at the outputs of the photoeells. l

Suicient for the purposesof the invention, the action of an astigmatic lens system may be explained approximately in the following manner. Por comparison, it will rst be recalled that in the case of an ideal anastigmatic lens system a4 point object produces a point image. This is indicated diagrammatically in FIG. 6 where a point object 1Q0 shown as being located on the optical axis 102 of a convex lens 104 sends out divergent rays which impinge upon the lens. Convergent rays from the lens form a point image 110.

FlGS. 7 and 8 serve to illustrate the approximate action of an astigmatic lens system suchas the lens system 22 of FIG, l and supplement the diagrammatic showings of FIGS. 1 and 3. As in FIG. 6, the point object 100 in FIG. 7* sends out divergent rays which impinge upon an astigmatic lens system which is represented schematically in top view atv112. The lens system forms a vertical image 114 at the location of the slotted screen and a horizontal image 116 at the coded mask. FIG. 8 shows lnzscrhemutic side view of the'same system illustrated in Point objects located o the axis 102 will form similar pairs of line images and a ray fom any point object to the middle of the tirst line image will pass approximately through the' middle of the second line image, thereby insuring the necessary one to one correspondence between the ordinate y on the curve 84 displayed on the face of the tube 20 in FIG; 1 and the vertical position of the horizontal line image 94 with respect to the coded mask 32, so that the photocells serve to read out the value of theprdinate of the curve to be analyzed.

, For a further detailed discussion of the properties of an astigmatic lens system and for additional forms of such systems, reference may be made to Introduction to Theoretical and Experimental Opties, uy Joseph Valasek, lohn Wiley Sons, 1949, beginning at page 45.

To summarize the operation of the system ot FIGS. 1 and 3, the cathode ray tube 20 displays on its face the curve 84 as indicated in FIG. 2. An astigmatic image of the curve is produced b'y the leus system 22 which lsv. A y. waveformanda-standardwaveform. t v

throws a beam upon the rotatable mirror 24. The mirrorsweeps the beam across the surface of the opaque mask 28, forming vertical line images of successive points of the curve upon the slit 30. The associated horizontal line images of successive points of the curve fall upon the surface of the coded mask 32 and cause combinations of the photoeells to be illuminated so that successive ordinate .values are represented by combinations of output currents `from the respective photocells in accordance withtbe code incorporated in the mask 32,

The magnetic reading and writing heads in the assembly 82 are placed so as to read the home pulse in track 64 at the time that the image of the left-hand edge of the usable portion of the cathode'ray tube face is projected `upon the slit 30. Then, as the mirror 24 continues to rotate, the output of the pbotocells is sampled the respective and.circuits each time a clock pulse in tra-ck 66 passes under the clock reading head 152 The samples are recorded directly and immediately in the respective data track 68, 70, ctc. on the drum 62. Photocell 34 feedsinformation into data track 68, cell 36 into *we s tlthoderaytnbe. Themirrorwmwbea tnckl,etc.,ecdspbotoeell feedngsputienlartnck. ilotatednreeptheimageotthefaceofthetubeaeron Whenthedevicehuccannedtheentireucefulfaeeof theslit-oneeineachmvolution, 'Ihm light emitted cathoderaytubeJllthesampledanddrgitizedy-datsh. aabypbosphoreseeneefromthefaceofthecathoderay beenstored cnthe magnetic drum, eachy-valnein a urbefrompostionsofincreasingabscissaorx-valueis 5 neparateregistercorrespondingtoitsnsociatedx-vllae.

s 'l'hestoredinformation maybe usedtorexamplqb Poruse with 4a vAS.ABP7-typtcathode ray tube having l useful tube face area measuring 3% inches and 2% inches vertically, a suitable astigmatic lens system might have, for example, a primary focal length of two and one-half inches and a secondary focal length of four and one-half inches. A fixed reflecting mirror 200 may be inserted in the path of the beam to conserve space as shown in FlG. 3 without interfering with the operation o! the system. The magnetic storage drum may be moutttul eoaxially with the rotating mirror and have a radius of 2,86 inches, for example. tube face then subtends approximately 20 degrees of the rotational arc o f the mirror and may be divided into 128 samples by means of 128 clock pulse marks in the clad track. The resulting packing density of the drum is 128 bits per inch along the periphery ofthe drum. Connoquently, 128 samples from the photocells may be recorded in one peripheral inch on the drum. Likewise the 128 clock pulse marls will occupy oneperipheral inch on the Y drum.

The number of samples may be more or less thanthe number of distinguishable ordinate values. The more samples, -in general, the better resolution and the more ordinate values distinguishable, in xeaenl, the better resolution vertically. Where the curve is steep,

the'more frequent the samples, the more accurate the analysis of the curve., Where tbe curve is less steep, le. frequent samples are needed for the saine For ordinary purposes, however, the number of samples N* unit horizontal length of the useful display area should be approximately the same as the number of ordinate values distinguishable per unit vertical. height of the useful display area.

The rst and second linear images are preferably mutually perpendiclar. lf there is a material departure from this angular difference between the images com plications are likely to arise in which the value of the ordinatewillbealectedbythevalueofthelbsciasalnd vice versa. It will also be evident that the tema hori-- zontal and vertical as applied to the respective imag. lproduced by the astigmatic lens system are relative and refer to any actual directions which are optically-ti' mechanically associated in one to one with the directions of the ordinate and ableiten respectively of the points on the curve.

While a cathare ray tube has been illustrated for cli-- able contrast of illumination in the region of the con- The image of the cathode ny" analyzing system as illustrated from the said coded masks have been drown whxcharesuitableforusewiththecomponentsofthe system illustrated, and whiehhave certain detinite ldvantages, it will be understood that other coded masks may advantageously be employed in some instances for causing the illumination striking the photocells to vary, y

g upon the ordinate of the point of the contour selected at a given moment, ao that the resulting output signals from the combination of photocells are indicative oftheordinateofthepoint.

The signals produced by the photocells may be used "to :et combinations of relays, to' control the punching of punch cards, to write a record into a memory device innde an automatic digital computer, etc., it not being necessary that the recording register or other recording device be mechanically coupled directly to the curveby' the showing of the shaft 26. As pointed out herein, however, there are denite advantages in the direct mechanical coupling.

Where a graph or curve is specified in the description or claims it is to be understood to include any suitable contour. While an illustrative form of apparatus and a method m accordance with the invention have been described and shown herein, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention. t

What is claimed is:

l. A system for analyzing a graph displayed on a substantially plane surface, said system comprising, in combination, an astigrnatic lens system having' first and second focal' regions wherein are formed linearly extended vertical and horizontal images respectively corresponding to a given point source, a slotted plate positioned h1 said rst focal region with the slot in a vertical direction, a rotatable mirror positioned to reflect upon said slot successive verticalv images derived from successive portions of said graph, and a plurality of photosensitive devices arranged in a horizontal array in said second focal region to receive a horizontal line image successive portions of the graph for alualyzing and encoding the vertical coordinate of the 2. A system for analyzing a graph displayed in luminous form on a substantially plane surface, said system comprising,- in combination, astigmatic optical means for producing a pair of linearly extended images from a point source of light on said graph, means comprising a rst mask having a slit therein aligned with one of said images to determine the abscissa of a given point on said graph and means comprising a second mask having apertures aligned with the other said image for using the other image to determine the'ordinate of the said 4gurenpcnnt.

3. Apparatus according to claim 2, in which the said astigmatic optical means comprises a pair of cylindrical lees having their axes angularly disposed to eachother.

4. Apparatus according to claim 3, in which the said cylindrical lenses are disposed with the respective cylindrical axes mutually perpendicular.

5. A system for determining digital values for points on a curve that is displayed in luminous form, comprising, in combination, an astigmatic lem system for producing a pair of linearly extended images from a given point of said curve, means including a tirst opaque mask having a slit aligned with one of said images to determine the abscissa of the given point, and means including a second opaque mask having a plurality of trans parent portions for determining the` ordinate of said given point.

6. A system for analyzing a curve displayed in luminous form on a substantially plane surface, said system comprising, in combination, an astigmatic lens system having first and second focal regions wherein are formed a pair of mutually perpendicular,F substantially linear y 8 imagescorrespondingtoasinglepointaormadotted masklocatedinsaidrstfocalregionandhavingalub' l sensitive means for sensing the relative position of the .saidlinearimageinsaidsecondfocalregim .7. A system for analyzing a curve displayed in liminous form on a substantially plane surface, said systun comprising, --in combination, an astigmatic lens system focusedupon said surface and having theproperty of forming a pair of images of a point'soutce, said images appearing at unequal distances from said lens system, the said images being angularly disposed with l respect to each other by an angle of rotation about the .ray through the center of the lens system, means-located between the lens system and the region of the said for rotating the beam from the lens system about an 1 axis perpendicular to said beam and parallel tc the nearer of said images, a mask located in the region ofthe nearer image and having a slit therein, said slit extending in the same direction as the said nearer image, whereby linear images of successive points on said curve are formed within said slit, and a coded mask located in the region of said farther image for sensing displacement of said farther image in a direction perpendicular to the direction of said farther image. 8. A system for reading and recording coordinates of a curve displayed on the face of a cathode ray tube comprising, in combination, astigmatic optical means for projecting a pair of linear images of any given point on said curve, said means having rst and second fom regions at diti'erent distances from said optical means, in which respective regions the image is linearly extended in diterent directions, rotating optical means 'for in effect sweeping said images through an angle in space, an opaque mask in the path of sweep of said images, said mask being located in the iirst focal region of the said astigmatic means and said mask'having a slit there in parallel to the direction of the image in said lirst focal region, c coded mask having a plurality of transparent portions, said coded mask being located in the second focal region of the said astigmaiic means, a plurality of photocells located behindsaid coded mask, each said cell being exposed to light through one or more of the transparent portions of said coded mask, a storage drum rotatably mounted in lixed angular relationship to said rotatable optical means, said drum including a plurality of storage tracks including a timing track, a plurality of reading-writing heads each individual to one of said tracks, a plurality of and circuit, first and second input circuits for said and circuits, means connecting the outputs of said photocells respectively to the rst input circuits of the and" circuits, means connecting the head for said timing track to the second inputs of all said andf circuits, and means connecting the outputs of the said and circuits to a plurality of storage tracks of said drum 9. A system for determining digital values for points on a curve, comprising, in combination, an sstigmatic j len's system having first and second focal regions wherein A are formed a pair of mutually perpendicular substantially linear images corresponding to a given point lens system being positioned to receive and transmit light from a eld of view including said curve, a slotted mask t located in said rst focal region and having a substantially linear slot therein extending parallel to said linear image in said region, a movable optical device located beyond said lens system positioned to direct arrimage of j successive points of said curve upon said slot in said l 9 10 focalxegionofdnnidutgmntclemsystmapheloetriedeviezstoprodueeoutputsigmhreprueatzdw nlityofpbmoelectcdevisloutedbehndndooded ofuidothercoordinzofsaidlelectedpontdld mask positioned respectively to receive light through said el'nve.

. transparent portions thereof, uid transparent portions of ,Y v

saidmaskbeingsolocatedwithrespeczxosaidphos Mmnwdinthekofupm electric devices that, for agven value of Ythe other codinan of said Selected point on nid cum, Bgm num UNITED STATES um the'region of said selected point passes through a par 1.931.852 Reichel et nl. Oct. 24. 1933 icula combinaon of said -transparent portions and 27,801,343 Johnson July 30, 1957 thereby energize: a particular combination of nid photo- 10 2.897.431 Shplh'l Jly 2.8', 1959 

